Chapter 14- Homeostasis Flashcards
Define homeostasis
The maintenance of a relatively constant internal environment for the cells in the body
List some of the physiological factors controlled by homeostasis
- Temperature
- water potential
- Glucose conc.
- pH blood
- Concentration of O2, CO2 in the blood
What could happen if temperature is not regulated:
low temp: Slows down metabolic reactions
High temp: can result to enzymes and transport proteins being denatured
What could happen if pH of blood is not regulated:
- enzymes will be affected and their functioning may slow down or could be denatured as a result
what is a receptor
- This is a cell OR tissue that receives a specific signal/ stimuli and communicates with the control centre by generating the CNS
What is a effector
- A tissue or organ that carries out an action with response to a stimuli
Describe how a stimulus is travelled to the effector
- The receptors will detect the stimulus
- The receptors will send this information from the stimulus to the central control in the brain or spinal cord.
- this information is known as input and upon receiving the input, the central control will instruct the effector to carry out an action
what refers to the set point
- The ideal value of a physiological factor that homeostasis tries to maintain
Nervous system VS Endocrine system
Nervous: It sends info in the form of electrical impulses along neurone
Endocrine: It uses chemical messengers such as hormones and travels in the form of long distancing cell signalling
Positive feedback VS Negative feedback
Positive: This does not work by keeping conditions constant but insteaad increasing the effect while the simulus increases
Negative: this tends to reduce the change by making it close to the set point as much as possible.
Define excretion
- The removal of toxic waste products from metabolic reactions in the body
Describe how CO2 is excreted in the body
- CO2 is continuously produced by respiring cells
- This CO2 is transported in the blood to the lungs where alveoli are present
- The CO2 is exchanged and diffuses through the capillaries to the alveoli and into the air we breathe out.
where is urea produced
- It is produced in the liver
Briefly describe deamination and the products
- This is the break down of excessive amino acids
- this is done by removing the amine group from the amino acids with an extra hydrogen atom
- the amine group combines with the hydrogen atom to create ammonia
- the keto acid that remains is taken to either the Krebs cycle or converted to glucose or fat
What does ammonia do to the body and how is its damage prevented
- Ammonia is highly toxic and can increase the pH
- This will affect the metabolic reactions in the cytoplasm
- This can also affect cell signalling in the brain
- The damage is prevented by converting ammonia to urea which is less toxic and less soluble
state 2 other excretory products other than urea
- Creatinine
- Uric acid
How is creatinine and uric acid formed
CREATININE: A substance known as creatine which is made in the liver. Most of this is used as creatine phosphate in the muscles while some is converted to creatinine
URIC ACID: This is made by the breakdown of purines from nucleotides
state the structure of the kidney from the outer most layer
- Capsule
- cortex
- medulla
- pelvis
- branch of renal artery
- branch of renal vein
- ureter
State the structures in the nephron and which are located in the cortex or medulla
- Bowmans capsule (cortex)
- Glomerulus (cortex)
- Efferent and afferent arteriole (cortex )
- Proximal convoluted tube (Cortex)
- descending and ascending limb of loop of henle (Medulla)
- distal convoluted tube ( cortex)
- Collecting duct ( both)
- pelvis
afferent arteriole vs efferent arteriole
afferent: arteriole leading to glomerular capillaries
efferent: leading away from glomerular capillaries
what are the 2 stages that the kidney makes urine in
- Selective reabsorption
- Ultrafiltration
Describe ultrafiltration step by step
- 1 Hydrostatic pressure builds up in the glomerulus due to wider afferent arteriole and narrower efferent arterioles
- 2 the hydrostatic pressure in the glomerulus is therefore higher than the Bowmans capsule
- 3 water will then go down its water potential gradient through the endothelium of the capillary and meet the basement membrane & podocytes, thus filtering the substances.
how are the Bowmans capsule and glomerulus adapted to fit ultrafiltration
- The holes in the capillary endothelium as well as the podocytes make it relatively easier for substances to pass through
- Basement membranes stop large proteins from passing through so act as a filter
What keeps the water potential low in the glomerulus compared to the capsule
- This is mainly due to larger plasma proteins not being able to pass through to the capsule and so, makes the filtrate much more concentrated in comparison
which solutes are reabsorbed in the PCT
- Glucose
- amino acids
- sodium ions
- chloride ions
- vitamins
State the adaptations of the cuboidal epithelial cells
- They have microvilli to increase the surface area for several co transporters
- They have several mitochondria to produce ATP to provide Na+-K+ pumps with energy in the basal membrane
- folded basal membrane that provide a large surface area for pumps
- tight conjunctions to avoid fluid from passing through.
Describe the selective reabsorption in PCT step by step
- 1 The Na+-K+ pumps are used to pump out sodium and few potassium ions in the basal membrane to the blood.
- 2 This results to a reduction in Na+ in the cell
- 3 therefore sodium ions will be co-transported from the filtrate to the cell with a glucose or amino acid molecule (secondary active transport)
- 4 Once inside the cell, glucose will be able to move down its gradient, through a transport protein into the blood and outside the cell.
Describe the water reabsorption in the PCT
- Due to the removal of these filtrates in the filtrate, it increases the water potential of the cell
- while the water potential of the blood lowered due to these solutes, water moves down its osmotic gradient
- the water and solutes are circulated through the blood.
What happens to some of the urea that doesn’t remain in the PCT
This urea gets passively reabsorbed by passing through cell surface membranes as urea is a very small molecule.
Describe the reabsorption that takes place in the Loop of Hence
- 1 Sodium and Chloride ions are actively transported out of the ascending limb into the tissue fluid
- 2 This decreases the water potential of the tissue fluid and so water moves down its gradient via osmosis from the descending limb
- 3 This ends up making the limb more concentrated with sodium and chloride ions and so they actively move out once the filtrate has reach the ascending limb.
Describe the reabsorption of water in the DCT and collecting duct
- 1 Due to the ascending limb losing sodium, chloride ions and urea e.t.c, it has a higher water potential
- 2 as the fluid moves to the DCT water moves down its osmotic gradient into the tissue fluid in the medulla
- 3 this ends up making the urine more concentrated as it reaches the collecting duct
Define osmoregulation
The control of water potential in the body fluid
describe what happens when water level decreases
- Osmoregulators in the hypothalamus sends a signal to the posterior pituitary gland and thereafter secretes the antidiurectic hormone
- ADH then travels in the blood to the target cells which are cells in the collecting duct
- the ADH acts on the luminal membrane and making them more permeable to water than usual
- this is brought about by increasing the water channels known as aquaporins. Vesicles are the ones that bring about these ready made channels
- ADH stimulates cyclic AMP(second messenger) after binding to the receptors on the cell
- cyclic AMP triggers a signalling cascade leading to the phosphorylation of aquaporins. The aquaporins are now activated and this causes the vesicles to move towards the luminal membrane and fuse with them
- This will result to an increase in the permeability of water and so water will move out of the collecting duct and into the tissue fluid `
Describe what happens when water level increases
- osmoreceptors will no longer stimulate ADH production and so aqauporins will move back into the cytoplasm, making water impermeable.
- this fluid will flow through the collecting duct without losing any water making the urine very dilute
why don’t collecting duct cells not respond immediately to the reduction in ADH receptors
- This is because it takes a relatively long time for ADH to dissolve in the blood (15-20mins) and once they don’t reach, it takes 10-15 minutes for aquaporins to leave the membrane
Which group of cells surround the pancreas and make up the tissue that acts as the homeostatic control of glucose levels
- islets of Langerhans
What are the 2 types of pancreatic cells that are involved in homeostasis of glucose
- Alpha cells which secrete glucagon
- Beta cells which secrete insulin
Describe what happens when blood glucose rises
- Beta cells respond by secreting insulin in the blood
- insulin acts as a signaling molecule and is transported to the target organs; the liver and muscles
- insulin binds to the cell receptors of these cells and this stimulates an increase in the absorption of glucose by having the vesicles carry glucose transport proteins (GLUT)
- GLUT allows glucose to enter into the cell
Glycogensis vs Gluconeogenesis
Glyco: this is the condensing of glucose into glycogen which will later be converted to glucose for respiration
Gluco: New glucose is made from amino acids and lipids
Describe what happens when blood glucose drops
- Alpha cells will detect this and release glucagon
- Glucagon binds into the liver cell receptors and this triggers the G protein
- The G protein will then activate adenylyl cyclase which catalyzes the conversion of ATP to cyclic AMP
- Cyclic AMP will bind to kinase enzymes which then trigger an enzyme cascade where glycogen phosphorylase enzyme will break down glycogen into glucose
what occurs during type 1 diabetes
The pancreas is incapable of secreting insulin due to:
- Autoimmune diseases
- lack of genes that code for insulin
What occurs during type 2 diabetes
when the pancreas secretes insulin but the liver and muscle cells do not respond properly. This will result to:
- Hunger and thirst
- cells will metabolise fats and proteins instead
what are the 2 urine analysis
- Dipsticks/test strips
- Biosensors
describe how biosensors work
- A small sample of blood is tested
- Small molecules in the plasma pass through the membrane.
- Glucose enters the active sites of the enzyme, glucose oxidase, which catalyses the reaction to produce gluconic acid and hydrogen peroxide.
- Hydrogen peroxide is oxidised at an electrode that detects electron transfers. This done with the enzyme Hydrogen peroxidase
- The electron flow is proportional to the number of glucose molecules in the blood. The biosensor will generate a reading from this
stomata open when:
- increase in light intensity
- Low CO2 levels
stomata close when:
- High CO2 levels
- Darkness
- low humidity
- high temperature
- reduction in water level
describe the opening of the stomata step by step
- the H+ ions being actively transported out of the guard cells via ATP powered proton pumps
- 2.The reduciton of H+ ions which carry a positive charge results to an electrochemical gradient being formed as there are more negative charges inside the guard cells than outside hence K+ will move in and Cl- also move inside the cell
- The increase of K+ will result to a decrease in W.P and hence water from outside of the cell will move into the cell via osmosis through the aquaporins
- The turgor pressure of the guard cells increase and the stomata opens
What makes Guard cells adapted for their role in opening and closing
The outer cell wall of the cell is thinner than the inner cell wall which is thicker
Describe the closing of the stomata step
- Hydrogen ion pumps stop and K+ ions will leave the cell, increasing the water potential of the cell
- Water will then leave the guard cells leaving it flaccid and the stomata closes
What are the effects of closing the stomata
- reduces the uptake of CO2 and
- rate of transpiration
what is abscisic acid
a stress hormone that causes the closure of the stomata in difficult conditions
How does abscisic acid function
- it binds to receptors that inhibit proton pumps and will stimulate the movement of Ca2+ in the cell
- Ca2+ will act as a second messenger and allow negative charged ions to move out of the cell and K+ ions will follow as well
- This will result in an increase of W.T in the cell and water will therefore move out of the cell making it flaccid
- the stomata will then close
